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Oncology > Basic concepts of Radiation Therapy > Flashcards

Basic concepts of Radiation Therapy Flashcards

1
Q

cancer in pet animals

A

Common, increasing prevalence
Every 2nd dog is euthanized due to „cancer“
Radiation therapy: second most used treatment modality in man
Model for research

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2
Q

resection “en bloc”

A

can’t remove just the tumour as tumour cells remain in the surrounding tissue

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3
Q

roles of radiation therapy

A 
INCOMPLETELY RESECTED TUMORS (treatment of choice) 
Non resectable tumors (results depending of tumor type) 
Pain control (Bone cancer/bone mets)
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4
Q

ionising radiation

A

Direct damage
Indirect damage (free radicals)
Unit for RT: Grey

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5
Q

reproductive death

A

DNA damaged - cell dies or lives but is unable to divide further

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6
Q

damage to DNA by ionising radiation effects

A

Mitosis delayed (10-100Gy)
Radiation damaged cells usually die after 1 or 2
attempts at mitosis
Tissues with high proliferation rate express radiation damage relatively quickly

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7
Q

most radiation sensitive cells

A 
undifferentiated
high mitotic rate
bone marrow 
intestinal crypt cells 
germinal layer of epidermis 
tumours
Tumoral mecanisms of DNA repair not as efficient as in normal cells
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8
Q

fractionation

A

The total dose of radiation used to treat a tumour is
usually divided into a number of fractions
spares normal tissues because it allows repair of sublethal damage and repopulation
increases damage to tumour because of reoxygenation + redistribution of cells into radiosensitive phases of cell cycle

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9
Q

4 R’s of radiation therapy

A

repair
repopulation
reoxygenation
redistribution

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10
Q

repair

A

tumor cells less able to repair DNA damage (Tumor cells are often oxygen + nutrient deficient)

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11
Q

repopulation

A

RT will often stimulate cell division.
Cells may respond to the death of adjacent cells by “accelerated repopulation”
In normal tissue this is kept under control by normal homeostatic mechanisms, but this is not true for the tumour.
need to give another dose to counteract repopulation + kill the cells

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12
Q

reoxygenation

A

The tumor contains a mix of aerated and hypoxic cells.
Immediately after RT, most cells in the tumor are hypoxic, but they tend to return at the pre-RT pattern because of reoxygenation

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13
Q

redistribution

A

Cells are more sensitive to RT in some phases: M-G2-G1-ES-LS
The remaining cells will be “synchronized” + eventually will move into a more sensitive phase
this is when to give next RT fraction

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14
Q

types of radiation used for radiotherapy

A

X-rays - Orthovoltage, 120-300kVp (not used much), Megavoltage, >1MeV “Linear accelerator”
Gamma rays - Cobalt-60, 1.2MeV
Particles - particles (electrons) in radioisotopes - Strontium-90: plesiotherapy, Iridium-192: brachytherapy

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15
Q

treatment machines

A

Cobalt-60-therapy unit

Linear accelerator

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16
Q

Cobalt-60-therapy unit

A

Radioactive source
Photons
Fixed energy (1.24 MV)
Technical requirements ↓

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17
Q

linear accelerator

A 
Variable energies 
electrons / photons 
No radioactivity 
High technical maintenance 
High accuracy
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18
Q

electron beam

A

Various energies possible (e.g. 5-16 MeV)
Rapid dose reduction (depending on energy)
Therapeutically useful depth: 1.5-5.6 cm
Single fields, simple dose calculation

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19
Q

photon beam

A 
High penetration 
Slow dose reduction  
Field arrangements necessary 
Penetration of normal tissue  
CT-based treatment planning
20
Q

goals of radiation therapy

A

curative/definitive (long term tumour control)

palliative (palliation, stabilisation of disease, pain reduction)

21
Q

curative radiation therapy

A

Absolute Indications - RT shows better results than other therapies
Relative Indications - RT shows same tumor control, but other advantages (functional, cosmetic)
Combination therapy - RT + surgery +/- chemo

22
Q

primary Tx modality

A

Brain tumor, tumor of head and neck (oral, nasal), MCT, epulis

23
Q

post Sx adjuvant RT

A

Mast cell tumor, Soft tissue sarcoma, Feline vaccine-associated sarcoma, etc.

24
Q

nasal tumours

A 
2/3 carcinomas; 1/3 sarcomas
median survival without treatment ~ 3 months 
surgery alone ~ 3-6 months 
radiation therapy alone: ~ 8-20 months 
RT + SX: 47 months
25
Q

brain tumours - pituitary tumours

A

85% of animals show rapid improvement of clinical signs
clinical signs, localization and size could not be shown to have prognostic significance
Very few side effects

26
Q

oral tumours

A

acantomatous epulides - 90% tumour control, 86% 3y PFI 4cm
oral scc - 45Gy, 1y PFI 75%
oral fsa - 33-67% 1y PFI

27
Q

squamous cell carcinoma - dog

A 
Middle aged dogs 
Rostral mandible 
Often cauliflower-like 
Local invasive 
Metastases - nontonsillar ~ 20%, tonsillar ~70% 
Prognosis -> site-dependent 
 rostral: local control -> cure 
 tonsillar: < 10% survive 1 year
28
Q

epulis

A

no metastases

90% cure rate with curative RT

29
Q

soft tissue sarcoma - dog

A

treat - surgery (+/- RT)

chemo

30
Q

feline injection-site sarcomas

A

Relationship between VAS and vaccination Incidence unknown 1/1000 – 1/10 000 cats
Tumor volume on contrast-enhanced CT ~ twice the volume measured using calipers on PE
Metastasis in 12-24%

31
Q

ISS therapy - surgery alone

A

10% cure rate with surgery alone (high probability of recurrence even with clean margins)
Surgery, conservative: recurrence after 2 months (median)
Surgery, radical: recurrence after 9 months (median)

32
Q

ISS therapy - surgery + RT

A

Recurrence: 600 days (median)
40% cure rate
Chemotherapy?
Prognostic factors - no. of surgeries, margins

33
Q

oral fibrosarcoma

A 
Histologically low-grade but biologically high-grade fsa
Golden retriever predisposed 
Maxilla > mandible 
V. invasive locally 
Often intact epithelium 
Metastasis in ~ 20% (lymph nodes, lungs)
34
Q

palliative radiation therapy

A

radiosensitive tumours w/high mets rate - histiocytic sarcoma, oral melanoma, hemangiosarcoma, Mast cell tumor grade III
mass effect - Large head and neck tumors, brain tumors, large sublumbar LN, prostatic tumor, etc
pain control - Osteosarcoma, metastatic bone tumors, etc

35
Q

malignant melanoma

A

Most common oral tumor in dogs
Mainly older dogs (mean 11.4 y)
Highly metastatic potential
1/3 amelanotic
RT: Overall response: 83%-94%, Complete response: 53%-69%
Negative prognostic factors - macroscopic disease, bone lysis, caudal location

36
Q

adverse effects of radiation TX

A

Some normal cells will die when they try to divide
RT effect may not be apparent until the irradiated cells attempt mitosis
Normal tissue included in radiation field
acute effect - will resolve rapidly dividing tissue: - Tumor, skin, mucosa, GI epithelium
late effect - permanent - Slowly dividing/non-dividing tissue: - Bone, muscle, brain, CNS, lens, retina, etc.

37
Q

acute side effects

A 
After the third week of radiation 
7-10 days post RT → maximum 
Normal tissue reactions 
mucous membranes - mucositis 
skin - alopecia, dermatitis 
eyes - keratitis / conjunctivitis 
[CNS - transient demyelination] 
Self limiting
Only symptomatic treatment
38
Q

acute side effects - skin/dermis

A

Target cells: stratum basale => erythema, scaly or moist dermatitis, alopecia
Treatment options - Protection from mechanical trauma (collar), Analgesia, no creams/ointments/gels

39
Q

acute side effects - mucous membranes

A

Hypersalivation, nasal discharge, mucositis (fibrinous plaques)
Pain - anorexia (rare in dogs, frequent in cats)
Treatment - Pain medication, antibiotics, feeding-tube (PEG) or esophageal tube, Metamucil / lactulose for colitis and proctitis

40
Q

acute side effects - eyes

A

Decreased tear production, conjunctivitis, blepharitis, cornea ulceration
Treatment - Optimmune / Vit. A eye ointment, Check tear production

41
Q

acute side effects - brain/spinal cord

A

Edema (8-12 weeks post RT)
Transient demyelination - transient „recurrence“ of neurological symptoms
Treatment - Corticosteroids

42
Q

late side effects

A 
Damage in stroma and vasculature 
Earliest onset: 6 months after RT 
Fibroses, contractions, strictures 
Non healing ulcerations 
Necrosis (bone, skin, CNS) 
Cataract, KCS 
Infarctions, hemorrhagias 
Therapeutical intervention difficult
43
Q

late side effects - skin/dermis

A

Damage of vasculature and fibroblasts
Fibrosis
Alopecia bzw. pigment changes

44
Q

late side effects - eyes

A

Cataract (clearing of fibres of lens not possible)

Chronic keratoconjunctivitis sicca

45
Q

late side effects - brain/spinal cord

A

Necrosis of white matter (6-18 months)
Vasculopathy (1-4 years)
Differentiation with diagnostic imaging difficult (side effect or recurrent disease?)
Try treatment with corticosteroids

Oncology (5 decks)

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